Location

Location ANSS

2020/06/19 20:42:21 38.170 -117.835 6.5 4.9 Nevada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2020/06/19 20:42:21:0  38.17 -117.83   6.5 4.9 Nevada
 
 Stations used:
   BK.DANT BK.LEGD BK.OVRO BK.SUTB BK.WELL BK.WINE CI.CCC 
   CI.CLC CI.CWC CI.FUR CI.GRA CI.GSC CI.HAR CI.ISA CI.LRL 
   CI.LUC2 CI.MWC CI.OSI CI.RAG CI.TIN CI.TPO CI.VES GS.MCA04 
   IM.NV31 LB.TPH NC.AFD NC.LDH NC.MDPB NN.BEK NN.CMK6 NN.CTC 
   NN.DSP NN.GMN NN.KVN NN.LHV NN.MCA06 NN.MPK NN.PAH NN.PIO 
   NN.PNT NN.PRN NN.Q09A NN.QSM NN.REDF NN.S11A NN.SHP NN.WAK 
   NN.WDEM NN.WLDB SN.HEL US.ELK US.TPNV UU.CCUT UU.LCMT 
   UU.PSUT UU.SZCU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 7.08e+22 dyne-cm
  Mw = 4.50 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      196    85   -165
   NP2      105    75    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.08e+22      7     330
    N   0.00e+00     74     214
    P  -7.08e+22     14      62

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.69e+22
       Mxy    -5.82e+22
       Mxz    -4.37e+20
       Myy    -3.39e+22
       Myz    -1.90e+22
       Mzz    -3.09e+21
                                                     
                                                     
                                                     
                                                     
                     #############-                  
                  T #############------              
              ###   ############----------           
             ##################------------          
           ####################--------------        
          ####################------------   -       
         ####################------------- P --      
        #####################-------------   ---     
        -###################--------------------     
       ----#################---------------------    
       --------############----------------------    
       ------------#######-----------------------    
       -----------------##-----------------------    
        -----------------######-----------------     
        -----------------#######################     
         ---------------#######################      
          --------------######################       
           -------------#####################        
             ----------####################          
              ---------###################           
                 ------################              
                     -#############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.09e+21  -4.37e+20   1.90e+22 
 -4.37e+20   3.69e+22   5.82e+22 
  1.90e+22   5.82e+22  -3.39e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200619204221/index.html
        

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is

      STK = 105
      DIP = 75
     RAKE = -5
       MW = 4.50
       HS = 10.0

The NDK file is 20200619204221.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMWR
UNR
 USGS/SLU Moment Tensor Solution
 ENS  2020/06/19 20:42:21:0  38.17 -117.83   6.5 4.9 Nevada
 
 Stations used:
   BK.DANT BK.LEGD BK.OVRO BK.SUTB BK.WELL BK.WINE CI.CCC 
   CI.CLC CI.CWC CI.FUR CI.GRA CI.GSC CI.HAR CI.ISA CI.LRL 
   CI.LUC2 CI.MWC CI.OSI CI.RAG CI.TIN CI.TPO CI.VES GS.MCA04 
   IM.NV31 LB.TPH NC.AFD NC.LDH NC.MDPB NN.BEK NN.CMK6 NN.CTC 
   NN.DSP NN.GMN NN.KVN NN.LHV NN.MCA06 NN.MPK NN.PAH NN.PIO 
   NN.PNT NN.PRN NN.Q09A NN.QSM NN.REDF NN.S11A NN.SHP NN.WAK 
   NN.WDEM NN.WLDB SN.HEL US.ELK US.TPNV UU.CCUT UU.LCMT 
   UU.PSUT UU.SZCU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 7.08e+22 dyne-cm
  Mw = 4.50 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      196    85   -165
   NP2      105    75    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.08e+22      7     330
    N   0.00e+00     74     214
    P  -7.08e+22     14      62

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.69e+22
       Mxy    -5.82e+22
       Mxz    -4.37e+20
       Myy    -3.39e+22
       Myz    -1.90e+22
       Mzz    -3.09e+21
                                                     
                                                     
                                                     
                                                     
                     #############-                  
                  T #############------              
              ###   ############----------           
             ##################------------          
           ####################--------------        
          ####################------------   -       
         ####################------------- P --      
        #####################-------------   ---     
        -###################--------------------     
       ----#################---------------------    
       --------############----------------------    
       ------------#######-----------------------    
       -----------------##-----------------------    
        -----------------######-----------------     
        -----------------#######################     
         ---------------#######################      
          --------------######################       
           -------------#####################        
             ----------####################          
              ---------###################           
                 ------################              
                     -#############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.09e+21  -4.37e+20   1.90e+22 
 -4.37e+20   3.69e+22   5.82e+22 
  1.90e+22   5.82e+22  -3.39e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200619204221/index.html
	
Regional Moment Tensor (Mwr)
Moment 6.579e+15 N-m
Magnitude 4.48 Mwr
Depth 11.0 km
Percent DC 90%
Half Duration -
Catalog US
Data Source US 2
Contributor US 2

Nodal Planes
Plane Strike Dip Rake
NP1 102 84 -8
NP2 193 82 -174
Principal Axes
Axis Value Plunge Azimuth
T 6.744e+15 N-m 1 148
N -0.344e+15 N-m 80 245
P -6.400e+15 N-m 10 57

        
Regional Moment Tensor (Mwr)
Moment 5.755e+15 N-m
Magnitude 4.44 Mwr
Depth 8.0 km
Percent DC 98%
Half Duration -
Catalog NN
Data Source NN 1
Contributor NN 1

Nodal Planes
Plane Strike Dip Rake
NP1 197 82 -163
NP2 104 73 -9

Principal Axes
Axis Value Plunge Azimuth
T 5.790e+15 N-m 6 330
N -0.072e+15 N-m 71 222
P -5.719e+15 N-m 18 61

        

Magnitudes

ML Magnitude


(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.


(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

Waveform Inversion using wvfgrd96

The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.
Location of broadband stations used for waveform inversion

The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.

The observed and predicted traces are filtered using the following gsac commands:

cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 n 3 
The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   105    75    10   4.13 0.2736
WVFGRD96    2.0   105    70    15   4.26 0.3638
WVFGRD96    3.0   105    75     5   4.29 0.4040
WVFGRD96    4.0   105    75     5   4.33 0.4335
WVFGRD96    5.0   105    75    -5   4.36 0.4598
WVFGRD96    6.0   105    75    -5   4.39 0.4824
WVFGRD96    7.0   105    75   -10   4.43 0.5011
WVFGRD96    8.0   105    75   -10   4.46 0.5161
WVFGRD96    9.0   105    75   -10   4.49 0.5251
WVFGRD96   10.0   105    75    -5   4.50 0.5289
WVFGRD96   11.0   105    75    -5   4.52 0.5282
WVFGRD96   12.0   105    80    -5   4.53 0.5243
WVFGRD96   13.0   105    80     0   4.54 0.5179
WVFGRD96   14.0   105    80     0   4.55 0.5099
WVFGRD96   15.0   105    80     0   4.56 0.4999
WVFGRD96   16.0   105    80     0   4.57 0.4897
WVFGRD96   17.0   105    80     5   4.58 0.4784
WVFGRD96   18.0   105    80     5   4.59 0.4675
WVFGRD96   19.0   105    80     5   4.60 0.4570
WVFGRD96   20.0   105    80     5   4.60 0.4464
WVFGRD96   21.0   105    80     5   4.61 0.4356
WVFGRD96   22.0   105    80     5   4.62 0.4256
WVFGRD96   23.0   105    75     5   4.62 0.4161
WVFGRD96   24.0   105    75     5   4.62 0.4069
WVFGRD96   25.0   105    75     5   4.63 0.3981
WVFGRD96   26.0   105    75     5   4.64 0.3900
WVFGRD96   27.0   105    75     5   4.64 0.3823
WVFGRD96   28.0   105    75     5   4.65 0.3749
WVFGRD96   29.0   105    75     5   4.65 0.3677

The best solution is

WVFGRD96   10.0   105    75    -5   4.50 0.5289

The mechanism correspond to the best fit is
Figure 1. Waveform inversion focal mechanism

The best fit as a function of depth is given in the following figure:

Figure 2. Depth sensitivity for waveform mechanism

The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted. Each observed-predicted component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed and because the velocity model used in the predictions may not be perfect. A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow. The lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).

The bandpass filter used in the processing and for the display was

cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 n 3 
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure.

A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:

Assuming only a mislocation, the time shifts are fit to a functional form:

 Time_shift = A + B cos Azimuth + C Sin Azimuth

The time shifts for this inversion lead to the next figure:

The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.

Discussion

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.

Velocity Model

The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
Model after     8 iterations
ISOTROPIC
KGS
FLAT EARTH
1-D
CONSTANT VELOCITY
LINE08
LINE09
LINE10
LINE11
      H(KM)   VP(KM/S)   VS(KM/S) RHO(GM/CC)         QP         QS       ETAP       ETAS      FREFP      FREFS
     1.9000     3.4065     2.0089     2.2150  0.302E-02  0.679E-02   0.00       0.00       1.00       1.00    
     6.1000     5.5445     3.2953     2.6089  0.349E-02  0.784E-02   0.00       0.00       1.00       1.00    
    13.0000     6.2708     3.7396     2.7812  0.212E-02  0.476E-02   0.00       0.00       1.00       1.00    
    19.0000     6.4075     3.7680     2.8223  0.111E-02  0.249E-02   0.00       0.00       1.00       1.00    
     0.0000     7.9000     4.6200     3.2760  0.164E-10  0.370E-10   0.00       0.00       1.00       1.00    

Quality Control

Here we tabulate the reasons for not using certain digital data sets

The following stations did not have a valid response files:

Last Changed Fri Jun 19 21:02:29 CDT 2020